The invention relates to regulating a fuel cell powered heating system.
A fuel cell is an electrochemical device that converts chemical energy produced by a reaction directly into thermal energy and electrical energy. For example, one type of fuel cell includes a proton exchange membrane (PEM), a membrane that may permit only protons to pass between an anode and a cathode of the fuel cell. At the anode, diatomic hydrogen (a fuel) is oxidized to produce hydrogen protons that pass through the PEM. The electrons produced by this oxidation travel through circuitry that is external to the fuel cell to form an electrical current. At the cathode, oxygen is reduced and reacts with the hydrogen protons to form water. The anodic and cathodic reactions are described by the following equations:
H2xe2x86x922H++2exe2x88x92 at the anode of the cell, and
O2+4H++4exe2x88x92xe2x86x922H2O at the cathode of the cell.
Besides electricity, the fuel cell also produces heat. Therefore, the fuel cell may be used to supply heat for purposes of regulating the temperature of a fluid, such as air or water, for example. By itself, a fuel cell provides relatively little heat. Therefore, for purposes of generating more heat, several fuel cells may be formed out of an arrangement called a fuel cell stack, an arrangement in which the fuel cells are electrically coupled together in series. Due to this electrical configuration, the power production capability of the fuel cell stack is also enhanced.
The fuel cell stack may include plates (graphite composite or metal plates, as examples) that are stacked one on top of the other, and each plate may be associated with more than one fuel cell of the stack. The plates may be made from a graphite composite material and include various channels and orifices to, as examples, route the reactants and products through the fuel cell stack. Several PEMs (each one being associated with a particular fuel cell) may be dispersed throughout the stack between the anodes and cathodes of the different fuel cells.
When used to produce heat, the fuel cell stack is capable of generating a large amount of power that may be transferred to an electrical utility""s power grid, for example. However, if not properly regulated, the transfer of power to the power grid may adversely affect the efficiency and health of the fuel cell stack.
In an embodiment of the invention, a method includes regulating a fuel cell system to produce a predetermined amount of heat. The fuel cell system also produces electrical energy that is transferred from the fuel cell system to a power grid. The minimum cell voltage of the fuel cell system is selected, and the rate at which the electrical energy is transferred to the power grid is regulated based on the minimum cell voltage. In some embodiments, the cell voltages are continually monitored during the regulation to dynamically determine the minimum cell voltage.
Advantages and other features of the invention will become apparent from the following description, from the drawing and from the claims.